/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package cn.emay.sdk.util.json.gson;

import java.lang.reflect.Field;
import java.util.Locale;

/**
 * An enumeration that defines a few standard naming conventions for JSON field
 * names. This enumeration should be used in conjunction with
 * {@link com.google.gson.GsonBuilder} to configure a
 * {@link com.google.gson.Gson} instance to properly translate Java field names
 * into the desired JSON field names.
 *
 * @author Inderjeet Singh
 * @author Joel Leitch
 */
public enum FieldNamingPolicy implements FieldNamingStrategy {

	/**
	 * Using this naming policy with Gson will ensure that the field name is
	 * unchanged.
	 */
	IDENTITY() {
		@Override
		public String translateName(Field f) {
			return f.getName();
		}
	},

	/**
	 * Using this naming policy with Gson will ensure that the first "letter" of the
	 * Java field name is capitalized when serialized to its JSON form.
	 *
	 * <p>
	 * Here's a few examples of the form "Java Field Name" ---> "JSON Field Name":
	 * </p>
	 * <ul>
	 * <li>someFieldName ---> SomeFieldName</li>
	 * <li>_someFieldName ---> _SomeFieldName</li>
	 * </ul>
	 */
	UPPER_CAMEL_CASE() {
		@Override
		public String translateName(Field f) {
			return upperCaseFirstLetter(f.getName());
		}
	},

	/**
	 * Using this naming policy with Gson will ensure that the first "letter" of the
	 * Java field name is capitalized when serialized to its JSON form and the words
	 * will be separated by a space.
	 *
	 * <p>
	 * Here's a few examples of the form "Java Field Name" ---> "JSON Field Name":
	 * </p>
	 * <ul>
	 * <li>someFieldName ---> Some Field Name</li>
	 * <li>_someFieldName ---> _Some Field Name</li>
	 * </ul>
	 *
	 * @since 1.4
	 */
	UPPER_CAMEL_CASE_WITH_SPACES() {
		@Override
		public String translateName(Field f) {
			return upperCaseFirstLetter(separateCamelCase(f.getName(), " "));
		}
	},

	/**
	 * Using this naming policy with Gson will modify the Java Field name from its
	 * camel cased form to a lower case field name where each word is separated by
	 * an underscore (_).
	 *
	 * <p>
	 * Here's a few examples of the form "Java Field Name" ---> "JSON Field Name":
	 * </p>
	 * <ul>
	 * <li>someFieldName ---> some_field_name</li>
	 * <li>_someFieldName ---> _some_field_name</li>
	 * <li>aStringField ---> a_string_field</li>
	 * <li>aURL ---> a_u_r_l</li>
	 * </ul>
	 */
	LOWER_CASE_WITH_UNDERSCORES() {
		@Override
		public String translateName(Field f) {
			return separateCamelCase(f.getName(), "_").toLowerCase(Locale.ENGLISH);
		}
	},

	/**
	 * Using this naming policy with Gson will modify the Java Field name from its
	 * camel cased form to a lower case field name where each word is separated by a
	 * dash (-).
	 *
	 * <p>
	 * Here's a few examples of the form "Java Field Name" ---> "JSON Field Name":
	 * </p>
	 * <ul>
	 * <li>someFieldName ---> some-field-name</li>
	 * <li>_someFieldName ---> _some-field-name</li>
	 * <li>aStringField ---> a-string-field</li>
	 * <li>aURL ---> a-u-r-l</li>
	 * </ul>
	 * Using dashes in JavaScript is not recommended since dash is also used for a
	 * minus sign in expressions. This requires that a field named with dashes is
	 * always accessed as a quoted property like {@code myobject['my-field']}.
	 * Accessing it as an object field {@code myobject.my-field} will result in an
	 * unintended javascript expression.
	 * 
	 * @since 1.4
	 */
	LOWER_CASE_WITH_DASHES() {
		@Override
		public String translateName(Field f) {
			return separateCamelCase(f.getName(), "-").toLowerCase(Locale.ENGLISH);
		}
	};

	/**
	 * Converts the field name that uses camel-case define word separation into
	 * separate words that are separated by the provided {@code separatorString}.
	 */
	static String separateCamelCase(String name, String separator) {
		StringBuilder translation = new StringBuilder();
		for (int i = 0; i < name.length(); i++) {
			char character = name.charAt(i);
			if (Character.isUpperCase(character) && translation.length() != 0) {
				translation.append(separator);
			}
			translation.append(character);
		}
		return translation.toString();
	}

	/**
	 * Ensures the JSON field names begins with an upper case letter.
	 */
	static String upperCaseFirstLetter(String name) {
		StringBuilder fieldNameBuilder = new StringBuilder();
		int index = 0;
		char firstCharacter = name.charAt(index);

		while (index < name.length() - 1) {
			if (Character.isLetter(firstCharacter)) {
				break;
			}

			fieldNameBuilder.append(firstCharacter);
			firstCharacter = name.charAt(++index);
		}

		if (index == name.length()) {
			return fieldNameBuilder.toString();
		}

		if (!Character.isUpperCase(firstCharacter)) {
			String modifiedTarget = modifyString(Character.toUpperCase(firstCharacter), name, ++index);
			return fieldNameBuilder.append(modifiedTarget).toString();
		} else {
			return name;
		}
	}

	private static String modifyString(char firstCharacter, String srcString, int indexOfSubstring) {
		return (indexOfSubstring < srcString.length()) ? firstCharacter + srcString.substring(indexOfSubstring) : String.valueOf(firstCharacter);
	}
}
